1. Field of the Invention
Embodiments of the present invention relate to power sources for computer systems. More specifically, embodiments of the present invention relate to power sources for computer systems with improved light-load efficiency.
2. Related Art
Energy Star is a government-backed program which has promulgated power consumption standards to help businesses and individuals protect the environment through energy efficiency. With the help of Energy Star, in 2006, Americans saved an estimated $6 billion on power bills.
The Energy Star standard for the power consumption of computer systems will soon be updated to version 4.0. This new Energy Star standard sets more stringent power consumption limits for “sleep,” “standby,” and “idle” operating modes. Many current computer systems do not comply with the Energy Star 4.0 power consumption limits. For example, as shown in FIG. 1, Apple Inc.'s MacBook™ 13″ (where the dimension in inches is the size of the MacBook's display screen) and MacBook Pro™ 15″ and 17″ fail several sub-standards within the Energy Star 4.0 standard. More specifically, both the MacBook and the MacBook Pro fail the Energy Star power consumption standard in both sleep mode and idle (or “standby”) mode.
Computer power system designers have spent a considerable amount of time optimizing the power supply systems in computer systems such as the MacBook. Unfortunately, most of the optimizations have been directed at “full power” operation. Hence, these optimizations generally have little effect on the computer system's power conversion efficiency in the low-power modes (and can even degrade the computer system's power conversion efficiency in these modes).
FIG. 2A presents a block diagram of a power system 200. As shown in FIG. 2A, power system 200 includes adapter 202, charger circuit 204, battery 206, and voltage regulators 208-218. Adapter 202 converts an AC signal from a power source (e.g., a common 120 VAC electrical outlet) to a 16.5 VDC signal which is in turn converted by charger circuit 204 into a 12.6 VDC signal. The 12.6 VDC signal is then used as an input for voltage regulators 208-218 as well as for charging battery 206. (Note that battery 206 provides power for the system when adapter 202 is not coupled to a power source. Because battery 206 does not output a constant voltage, regulators 208-218 are typically designed to operate across a range of input voltage levels, (e.g., between 9 V and 12.6 V).)
FIG. 2B presents an exemplary power conversion efficiency curve (not to scale) for the power system in FIG. 2A. As can be seen in FIG. 2B, the power system has been optimized for full-power operation. Hence, the power conversion efficiency is approximately 90% for full-power operating currents of 6-8 A. Unfortunately, the power conversion efficiency drops below 40% for low-power currents below 100 mA.
Hence, what is needed is a power system for a computer system that operates without the above-described problems.